JPH0456873B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing solvent refined coal. There, coal is liquefied and solid and liquid products are produced by subjecting the coal to a hydrogen-donating solvent (hereinafter referred to as solvent) at high temperature and pressure in the presence of hydrogen-rich gas. This process is called SRC-1, which stands for Solvent Refined Coal with the acronym "SRC."

The United States Government has rights in this invention pursuant to Contract No. DE-AC05-780R03054 awarded by the United States Department of Energy.

In this process, following solvation, the product is separated into gaseous materials, distillate fractions and vacuum distillation bottoms. This vacuum distillation bottoms contains carryover minerals and unconverted coal macerals, which are separated in the deashing step. A coal product stream is recovered from the solids removal process. This coal product stream is free of ash material and unconverted coal and has an essentially low sulfur content. This material is therefore ideal for use in combustion applications under environmentally acceptable conditions.

SRC-1 pilots at Wilsonville, Alabama and Fort Lewis, Washington.
The plant is already operating with a coal liquefaction reactor (also known as a melter) equipped with a preheater. Some coal liquefaction reaction takes place in both of these vessels. Coal slurry in recycled solvent under hydrogen pressure passes through this preheater. There, the temperature is raised from room temperature to over 750 degrees Celsius. The heated slurry is sent to a reactor where the reaction of hydrogen gas, coal, and solvent occurs at temperatures in excess of 780°C and pressures in excess of 1000 psia. This liquefaction reaction includes desulfurization, solvent generation, rehydrogenation, etc.

As long as hydrogen gas is present, the rate of reaction that produces asphaltenes and oil from molten coal is greater than the retrograde repolymerization reaction that produces coke from low molecular weight products. However, at the reactor outlet it is necessary to separate the gas phase containing hydrogen from the slurry phase containing soluble coal product and solid residue. This separation is performed as the first step in reaction product separation. It is known that in the absence of hydrogen gas, coke formation can occur and preasphaltenes are produced by repolymerization. These undesirable reactions are more likely to occur when the temperature is high and the residence time is long.

The problem of coke formation in the separator separating the effluent from the reactor is seen at the Wilsonville pilot plant when operating at or near reactor temperature. At Wilsonville,
Coke formation at the separator outlet is expected to occur when operating at 800°C, and this problem is not encountered when operating at temperatures below 780°C.

One method already used to prevent retrograde reactions is to directly cool the entire coal reactor effluent by heat exchange or quenching. These operations have been adopted in the operation of the Wilsonville and Fortrewis pilot plants. More specifically, the coal liquefaction reaction occurs at temperatures ranging from 800 to 880〓;
The three-phase effluent is then cooled to a temperature sufficiently low to prevent coke formation prior to phase separation, generally below 780°C. In the SKC-1 demonstration plant design, cooling of this effluent is accomplished by using recycled solvent. Therefore, conventional methods involve cooling the entire reaction product stream exiting the reactor, which is inherently inefficient.

A general object of the present invention is to provide a coal liquefaction cooling method that inhibits coke formation while minimizing the loss of thermal efficiency of the coal liquefaction process. Briefly, the improved process of the present invention involves rapidly cooling the liquid-solid products of the coal liquefaction reaction without cooling the associated vapor stream, thereby preventing coke formation and retrograde reactions. This quenching is accomplished by recycling a somewhat cooled portion of the liquid-solid mixture to the lower region of the phase separator. This phase separator separates vapor from the liquid and solid products exiting the coal reactor. This recycle stream is introduced below the gas-liquid interface within the separator. This cooling is achieved by direct mixing with the non-volatile liquefied coal recirculation cooling stream, so there is no evaporation or foaming phenomenon that would cause the cooling stream to turn into hot vapor.
Therefore, inconveniences such as cooling the steam can be avoided.

According to the method of the invention, heat is separated and recovered from the vapor phase of the reaction product, such as the process solvent. The process solvent can be reheated to near reaction temperature and recycled directly to the reaction system. Heat recovery can therefore be made at the highest possible temperature without the essential strain of cooling the three-phase mixture in a heat exchanger (as is the case in the prior art). Moreover, this heat recovery is performed at a higher rate than the thermal efficiency when cooling the entire reaction product as in the conventional method.

Raw coal, typically finely ground coal, is mixed with the circulating solvent in the slurry mixing tank 10 at a ratio of 1:1.2 to
Mixed in a 1:3 ratio. Slurry from tank 10 is passed to pump unit 12. The pump unit pushes the slurry to pressures in the range of 1000 to 3000 psia. The pressurized slurry is heated by a heat exchanger 14 to an intermediate temperature in the range of 400-500°C. The heated recycle solvent passes through the heat exchanger while exchanging heat with the slurry. The heated slurry is mixed with a first hydrogen gas stream from line 15. This three-phase gas slurry stream is then directed to a preheating system comprising an externally heated tubular reactor 16. The three-phase mixture is heated to reaction temperature in the preheater. A second hydrogen gas stream is added to the preheated slurry via line 17 and the mixture is passed to the coal liquefaction stage. There, the slurry is conveyed to coal reactor 18. The reactor 18 comprises one or more tubular vessels that operate in an adiabatic manner without adding substantial external heat. In this reactor 18, the coal liquefaction reaction takes place at a temperature in the range of 800-880°C. The temperature distribution within the reactor is controlled by intermediate injection of cooled recycled hydrogen gas through line 70 in the lower part of the reactor over a temperature range of 150 to 250°C.

According to the method of the invention, the effluent from the reactor 18 is fed directly to the gas slurry phase separator 20 via line 19 without being cooled. This gas phase is removed from separator 20 via line 22 and heats the hydrogen gas which passes from heat exchanger 29 to lines 15 and 17. The process is then recirculated as shown.

The separator 20 is a cylindrical container and has a conical portion 21 below it. The system is designed such that the inlet to separator 20 is above the slurry level (labeled 23).

According to the process of the present invention, the hot slurry entering separator 20 at a temperature ranging from about 800 to 880° is reduced to about 540° to 540° at a temperature sufficiently low (less than about 780°) to suppress coke formation by the recirculating slurry stream. Over a temperature range of 700°, preferably cooled to about 600°. Also, the residence time of the slurry at elevated temperatures in the absence of hydrogen is minimized by immediately mixing with the coal recycle slurry stream. At the end of this, the effluent slurry exiting the bottom end of section 21 of separator 20 is split into two streams. One passes through loop 30 to pump 32 . This pump directs this flow to heat exchanger 34. In this heat exchanger, this stream is cooled by exchanging heat with the cooled recycled solvent flowing in line 36 as shown. For purposes of this invention, "chilled recirculated solvent"
The expression ``not heated'' means about 350~450〓
means a recycled solvent stream that is at or near a temperature over a range of . This solvent stream leaves the separation system at this temperature after distillation. The slurry is cooled by recycled process solvent in heat exchanger 34 and returns from heat exchanger 34 to section 21 of separator 20. The recycled process solvent is correspondingly heated to a temperature of 700 to 750°C in heat exchanger 34 and can be used to preheat the slurry fed to the reactor. The temperature and flow of the recirculated slurry stream are selected to provide a flow that will cause effective mixing with the hot slurry in separator 20. The preferred operating conditions for slurry cooling recirculation are:
25 of the standard slurry stream from separator 20.
~75%, and the cooling flow of the slurry is correspondingly cooled to 540-700%.

A second portion of the effluent slurry from separator 20 is sent via line 40 to heat exchanger 48 . Here, this stream is typically approximately
It is cooled to a temperature of 750㎓. This temperature is suitable for subsequent vapor separation and pressure reduction in distillation systems without the need for reheating, and this cooled slurry is fed to such systems via line 46. Ru.

The heated recycle solvent stream through heat exchangers 34 and 48 passes through combined line 50 to line 52. Line 52 carries the solvent to heat exchanger 14 , from where it is fed via line 53 to tank 10 . The gas phase exiting heat exchanger 29 also passes through heat exchanger 60 and from line 56 to line 5.
Go to 2 Cooling Recycle Step Increase the temperature of the solvent.

As mentioned above, according to typical conventional methods, the effluent from the reactor is passed directly to a heat exchanger and cooled before going to a three-phase separator. It is clear that the method of the present invention has several important advantages over this conventional method. A first advantage of the process of the invention is that coke formation is avoided by minimizing residence time at elevated temperatures in the absence of hydrogen. A second important advantage of the process of the invention is that it maximizes the temperature at which heat can be recovered from the reactor effluent without coke formation. A third advantage is that it avoids the difficulties associated with cooling three-phase effluents of the type leaving the reactor.

The foregoing description is a summary of the method and describes its essential operations, and those skilled in the art will understand the standard techniques required for the necessary valves, pumps, pressurization equipment, and other such systems. It goes without saying that you know where to place your tools and how to use them.

The present invention will be described below based on one embodiment, but it goes without saying that this embodiment is merely illustrative and is not intended to be limiting.

Example The method of the present invention will be described with reference to the figures.

Solvent refined coal (SKC) by SRC-I process
To produce this, 5600 T/D (tons/day) of coal is ground to a particle size of less than 200 mesh. This material is slurried by mixing with 9000 T/D of recycled aromatic process solvent. This solvent has a boiling point in the range of 400-900㎓ under atmospheric pressure.
This slurry is heated to a pressure slightly above atmospheric pressure.
Prepared in one or more stirred vessels at a temperature of 400°C.

This slurry is divided into 6 parallel streams and pumped to 2900 psig using a combination of centrifuge and reciprocating pump.
is pumped to a pressure of This slurry is then heated to a temperature of 500°C in a series of heat exchangers.

Heat recirculated hydrogen gas at a temperature of 800㎓ is 135T/
It is mixed with the slurry in proportions D to produce a three-phase mixture of coal, oil and gas before entering the preheating furnace. In this preheating furnace, the mixture is heated to a temperature of 760°C. In the preheating furnace, melting of the coal and various reactions that produce SRC, aromatic oils, and residue materials begin.

The preheated three-phase mixture is further heated before entering the first of the two coal liquefaction reactors.
Mixed with 135T/D of thermally recycled hydrogen gas. The coal liquefaction process in these reactors is completed at a temperature of 840° and a pressure of 2600 psig, producing SRC, aromatic oil, residual ash, undissolved coal, and gaseous reaction products. The temperature distribution within these reactors is further controlled by intermediate injection of 135 T/D of cooled recycle hydrogen gas into the lower part of the reactors.

The effluent three-phase streams from these reactors are passed directly to a separator at a temperature of 840°. There, the gas phase is separated from the slurry phase. 840〓Big cutlet
The slurry phase at a flow rate of 12000 T/D is mixed with a recirculated slurry stream of 6000 T/D at a temperature of 600° below the gas-liquid interface of the separator to form a mixed slurry stream. This slurry stream exits the separator at a temperature just below 780° and under a pressure of about 2550 psig. The separated gas stream exits this separator upwardly at a temperature close to 840°C.

The slurry stream exiting the separator is split into a product stream and a recycle stream. Each of these flows is 12000T/
D and 6000T/D. This recycle stream is pumped to a heat exchanger where it is cooled from 780 to 600 with the cooled recycle process solvent (i.e., 400). This cooled recycle slurry is then returned directly below the liquid interface of the separator.

The product slurry stream from the separator is combined with another section of cooled recycle process solvent before being further processed by phase separation and distillation to recover the SRC and aromatic oil products, recycle solvent and residual solids. It is cooled down to 750㎓ by heat exchange between.

The upper hydrogen, gaseous reaction products and volatile oil streams pass sequentially through two heat exchange systems with a total flow rate of 3600 T/D. In this heat exchange system, the gas is cooled and condenses the light oil and aqueous component mixture. Cooling takes place in a heat exchanger with recycled hydrogen gas. This hydrogen gas is preheated to 800 °C before being reinjected into the coal slurry prior to the reactor. Cooling of the gas also takes place in a further heat exchanger with cooled recycled process solvent.

[Brief explanation of drawings]

The figure is a general flow diagram of a preferred embodiment of the invention. 10... Slurry mixing tank, 12, 32... Pump, 14, 29, 34, 48, 60... Heat exchanger,
16...Reactor, 18...Coal reactor, 20...Separator.

Claims (1)

[Claims] 1. A method for producing solvent-refined coal in which a slurry of finely ground lime in a process solvent is sent to a high-temperature, high-pressure coal liquefaction reactor in the presence of hydrogen-rich gas via a preheater, directing the effluent to a gas-slurry phase separator and recycling the slurry from the separator through a cooling heat exchanger to the slurry phase of the separator to cool the slurry and reduce coke formation; Including coal liquefaction cooling method. 2. A process for producing solvent refined coal in which a slurry of finely ground lime in a process solvent is sent via a preheater to a high temperature, high pressure coal liquefaction reactor in the presence of hydrogen rich gas, the effluent from the reactor being passed to a gas slurry. direct to a phase separator; recirculating the slurry from the separator through a cooling heat exchanger to the slurry phase of the separator to cool the slurry and reduce coke formation; and removing the gas phase from the separator. A method of cooling coal to liquefaction comprising removing the gas phase and passing the gas phase through a heat exchanger to heat the process stream. 3. The method of claim 2, wherein said process stream is hydrogen gas, which is directed to a process solvent that is fed to said reactor. 4. The method of claim 3, wherein the gas phase is passed from a first heat exchanger to a second heat exchanger, through which it passes while exchanging heat with a cooling process solvent. 5. The method of claim 1, wherein the effluent is sent from the reactor to the separator without cooling. 6. The method of claim 1, wherein the slurry phase of the separator is cooled to a temperature of about 780°C or less. 7. The recycled slurry is withdrawn from the bottom of the separator and pumped to a heat exchanger through which a cooled recycled solvent is passed in heat exchange with the slurry to cool the slurry to a temperature of about 540 to 750°C. 2. The method of claim 1, wherein the method is returned to the separator at 8. The method of claim 7, wherein the slurry phase of the separator is cooled to a temperature of about 780°C or less. 9. The method of claim 7, wherein a portion of the recycled slurry withdrawn from the bottom of the separator is passed through a heat exchanger therethrough in exchange of heat with a cooling process solvent.